Composite hole transport material for flexible perovskite solar cell and preparation method and application thereof

Abstract

The invention provides a composite hole transport material for a flexible perovskite solar cell as well as a preparation method and application of the composite hole transport material. The composite hole transport material comprises polyacrylamide, lithium chloride and cellulose nanofibers coated with PEDOT: PSS (poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate)). By compounding polyacrylamide, lithium chloride and PEDOT: PSS coated cellulose nanofibers, the obtained composite hole transport material has the advantages of high conductivity, high mechanical strength and the like, and when the composite hole transport material is applied to a flexible perovskite solar cell, the bending resistance of the cell can be greatly improved; and the hole extraction and transmission performance can be improved, so that the photoelectric performance of the flexible perovskite solar cell can be obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a composite hole transport material for flexible perovskite solar cells, its preparation method, and its application. Background Technology

[0002] In recent years, the market demand for flexible perovskite solar cells (FPSC) has been increasing, mainly due to the characteristics of perovskite thin films, such as low-temperature fabrication, light weight, flexibility, and compatibility with various curved surfaces.

[0003] The most significant characteristics of flexible perovskite solar cells (FPSCs) are their flexibility and resilience. Traditionally, resilience refers to a material's ability to deform under external force and recover from deformation after the force is removed. The resilience of an object is related to the inherent properties of the material. Therefore, obtaining highly resilient FPSCs requires specific requirements regarding chemical composition and preparation methods.

[0004] For FPSCs, the main components include a flexible substrate, electrodes, perovskite light-absorbing materials, and charge transport materials. Among these, charge transport materials include electron transport materials (ETM) and hole transport materials (HTM). To achieve efficient and stable flexible devices, charge transport materials should possess the following characteristics: 1) ability to be fabricated at low temperatures; 2) excellent carrier extraction capability; 3) good interfacial contact; 4) low carrier transport resistance; 5) suitable energy levels; and 6) high resilience. Furthermore, the selection of hole transport materials must also meet the requirements of solution processing.

[0005] Currently, commonly used charge transport layer materials (HTMs) mainly include poly(3-hexylthiophene) (P3HT), poly(bis(4-phenyl)(2,4,6-bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA), poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS), and inorganic materials such as NiOx. However, these charge transport layer materials often have poor flexibility and weak contact with adjacent layers. This causes the recoverability of these charge transport layer materials to decrease rapidly during repeated bending of flexible perovskite solar cells, leading to a decline in charge extraction and transport efficiency within the device, increased interfacial recombination, and ultimately a significant degradation in the photoelectric conversion efficiency, decreased operational stability, and shortened lifespan of the flexible solar cell.

[0006] Therefore, there is an urgent need to design a hole transport material with strong conductivity and strong mechanical strength, so that flexible perovskite solar cells can significantly improve their bending resistance while ensuring excellent photoelectric performance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a composite hole transport material for flexible perovskite solar cells, its preparation method, and its application. This invention involves combining polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers to obtain a composite hole transport material with advantages such as strong conductivity and high mechanical strength. Using this material in flexible perovskite solar cells not only significantly improves the cell's bending resistance but also enhances hole extraction and transport performance, resulting in a marked improvement in the photoelectric performance of flexible perovskite solar cells.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a composite hole transport material for flexible perovskite solar cells, the composite hole transport material comprising polyacrylamide, lithium chloride and cellulose nanofibers coated with PEDOT:PSS.

[0009] This invention constructs a composite gel-like hole transport material by combining polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers. Polyacrylamide, as a flexible polymer matrix, provides a stretchable network framework and good interfacial compatibility. Lithium chloride not only effectively enhances the overall conductivity of the material as an ionic conductor, but its strong hydration further enhances the interaction between the colloidal phase and water molecules, thus significantly improving the mechanical stability of the material. The PEDOT:PSS-coated cellulose nanofibers simultaneously play a dual role in nano-reinforcement and conductive network construction: the cellulose nanofibers introduce abundant hydrogen bonding sites at the microscopic level, significantly improving the tensile strength and toughness of the material, while the PEDOT:PSS coating on their surface forms a continuous and efficient charge transport pathway in the system, synergistically improving hole mobility. In summary, the synergistic effect of these three components greatly improves the conductivity, mechanical strength, and environmental stability of the composite hole transport material.

[0010] The composite hole transport material provided by this invention, when applied to flexible perovskite solar cells, exhibits excellent mechanical flexibility and high interfacial adhesion, effectively buffering bending stress and suppressing microcrack formation and interfacial delamination. This significantly improves the repeated bending resistance and mechanical reliability of flexible perovskite solar cells. Simultaneously, it facilitates efficient and stable hole extraction and transport, reducing interfacial recombination losses. Therefore, flexible perovskite solar cells using this composite hole transport material maintain excellent photoelectric conversion efficiency and operational stability even after multiple bending cycles, resulting in a significant improvement in overall performance.

[0011] Preferably, based on the total mass of the composite hole transport material, the mass percentage of lithium chloride is 5%-25%, for example, it can be 5%, 10%, 15%, 20% or 25%, etc.

[0012] Preferably, based on the total mass of the composite hole transport material, the mass percentage of the polyacrylamide is 15%-45%, for example, it can be 15%, 20%, 25%, 30%, 35%, 40% or 45%, etc.

[0013] Preferably, in the composite hole transport material, the mass ratio of polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers is (0.3-0.6):(0.08-0.5):1, wherein the polyacrylamide is selected in the range of "0.3-0.6", for example, 0.3, 0.4, 0.5, or 0.6, and the lithium chloride is selected in the range of "0.08-0.5", for example, 0.08, 0.1, 0.2, 0.3, 0.4, or 0.5.

[0014] Preferably, in the PEDOT:PSS-coated cellulose nanofibers, the mass ratio of PEDOT:PSS to cellulose nanofibers is 1:(1.2-1.8), for example, it can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7 or 1:1.8, etc.

[0015] Preferably, in the PEDOT:PSS-coated cellulose nanofibers, the diameter of the cellulose nanofibers is 20nm-80nm, for example, 20nm, 40nm, 60nm or 80nm, and the length is 500nm-1500nm, for example, 500nm, 800nm, 1000nm, 1200nm or 1500nm.

[0016] In a second aspect, the present invention provides a method for preparing a composite hole transport material for flexible perovskite solar cells as described in the first aspect, the method comprising the following steps: Prepare a PEDOT:PSS-coated cellulose nanofiber suspension.

[0017] The cellulose nanofiber suspension coated with PEDOT:PSS, acrylamide monomer, and lithium chloride were mixed to obtain a dispersion.

[0018] The dispersion, crosslinking agent, initiator and catalyst are mixed and polymerized to obtain the composite hole transport material.

[0019] Preferably, the preparation steps of the PEDOT:PSS-coated cellulose nanofiber suspension include: (a) Cellulose nanofibers, 3,4-ethylenedioxythiophene, sodium polystyrene sulfonate and an oxidant are mixed and oxidized to obtain an intermediate solution.

[0020] (b) The intermediate solution, oxidant and initiator are mixed and reacted to obtain a cellulose nanofiber suspension coated with PEDOT:PSS.

[0021] Preferably, the concentration of the PEDOT:PSS-coated cellulose nanofiber suspension is 0.4wt%-0.6wt%, for example, it can be 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt% or 0.6wt%, etc.

[0022] Preferably, the volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:(2-4) g:(0.5-3) g, wherein the acrylamide monomer is selected in the range of "(2-4) g", for example, 2 g, 3 g, or 4 g, and the lithium chloride is selected in the range of "(0.5-3) g", for example, 0.5 g, 1 g, 1.5 g, 2 g, 2.5 g, or 3 g.

[0023] Preferably, the polymerization reaction temperature is room temperature. For example, room temperature can be 25±5℃, such as 20℃, 25℃, or 30℃.

[0024] Preferably, the polymerization reaction takes 20-40 minutes, for example, 20 minutes, 30 minutes, or 40 minutes.

[0025] Preferably, the preparation method includes the following steps: (1) Preparation of PEDOT:PSS-coated cellulose nanofiber suspension, the preparation steps include: (a) 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate are added to cellulose nanofibers to obtain a mixture; the mixture is oxidized under stirring conditions with an oxidant to obtain an intermediate solution; wherein the oxidant includes tetramethylpiperidine oxide.

[0026] (b) An oxidant and an initiator are added to the intermediate solution and stirred and mixed. The mixture is then reacted at room temperature (e.g., 15-25°C, such as 15°C, 20°C, or 25°C) for 16-20 hours (e.g., 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours). After the reaction is completed, the mixture is washed and sonicated to obtain a PEDOT:PSS-coated cellulose nanofiber suspension. The oxidant includes ferric chloride, the initiator includes ammonium persulfate, and the concentration of the PEDOT:PSS-coated cellulose nanofiber suspension is 0.4 wt%-0.6 wt%.

[0027] (2) Acrylamide was added to the cellulose nanofiber suspension coated with PEDOT:PSS, and then lithium chloride was added and stirred to obtain a dispersion.

[0028] The volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:(2-4) g:(0.5-3) g.

[0029] (3) Under stirring conditions, a crosslinking agent, an initiator and a catalyst are added to the dispersion and mixed. Then, a polymerization reaction is carried out at room temperature for 20 min-40 min to obtain a composite hole transport material.

[0030] The crosslinking agent includes methylenebisacrylamide, the initiator includes ammonium persulfate, and the catalyst includes tetramethylethylenediamine.

[0031] Thirdly, the present invention provides a flexible perovskite solar cell, the flexible perovskite solar cell comprising a flexible conductive substrate, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer and electrodes stacked together.

[0032] The material of the hole transport layer is the composite hole transport material for flexible perovskite solar cells described in the first aspect.

[0033] Preferably, the flexible conductive substrate is made of any one of polyethylene terephthalate, polyethylene naphthalate, or colorless polyimide.

[0034] Preferably, the thickness of the hole transport layer is 30nm-50nm, for example, it can be 30nm, 40nm or 50nm.

[0035] Preferably, the chemical formula of the perovskite light-absorbing layer is ABX3, wherein A includes any one or a combination of at least two of formamidinium ions, methylamine ions, cesium ions, or rubidium ions; B includes any one or a combination of at least two of lead ions, tin ions, or germanium ions; and X includes any one or a combination of at least two of chloride ions, bromide ions, or iodide ions.

[0036] Preferably, the thickness of the perovskite light-absorbing layer is 400nm-700nm, for example, it can be 400nm, 500nm, 600nm or 700nm.

[0037] Preferably, the electron transport layer is made of an n-type semiconductor material, wherein the n-type semiconductor material includes C 60 Any one of PCBM, TiO2, SnO2, ZnO, or ZnO-ZnS.

[0038] Preferably, the electrode includes any one of an Al electrode, an Au electrode, an Ag electrode, or a carbon electrode.

[0039] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0040] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention constructs a composite gel-like hole transport material by combining polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers. Polyacrylamide, as a flexible polymer matrix, provides a stretchable network framework and good interfacial compatibility; lithium chloride not only effectively enhances the overall conductivity of the material as an ionic conductor, but its strong hydration further enhances the interaction between the colloidal phase and water molecules, thus significantly improving the mechanical stability of the material; the PEDOT:PSS-coated cellulose nanofibers simultaneously play a dual role in nano-reinforcement and conductive network construction: the cellulose nanofibers introduce abundant hydrogen bonding sites at the microscopic level, significantly improving the tensile strength and toughness of the material, while the PEDOT:PSS coating on its surface can form a continuous and efficient charge transport pathway in the system, synergistically improving hole mobility. In summary, the synergistic effect of the three components greatly improves the conductivity, mechanical strength, and environmental stability of the composite hole transport material.

[0041] (2) When the composite hole transport material provided by this invention is applied to flexible perovskite solar cells, its excellent mechanical flexibility and high interfacial adhesion can effectively buffer bending stress, suppress microcrack generation and interfacial peeling, thereby significantly improving the repeated bending resistance and mechanical reliability of flexible perovskite solar cells. At the same time, it is also conducive to achieving efficient and stable hole extraction and transport, and reducing interfacial recombination loss. Therefore, the flexible perovskite solar cells using this composite hole transport material can still maintain excellent photoelectric conversion efficiency and working stability after multiple bends, and the overall performance is significantly improved. Attached Figure Description

[0042] Figure 1 The images show the comparative UV spectra of the perovskite light-absorbing layers prepared in Example 1 and Comparative Example 1 of this invention.

[0043] Figure 2 The images show the comparative fluorescence spectra of the perovskite absorbing layers prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] It should be understood that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0046] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] In one specific embodiment, the present invention provides a composite hole transport material for flexible perovskite solar cells, the composite hole transport material comprising polyacrylamide, lithium chloride and cellulose nanofibers coated with PEDOT:PSS.

[0048] This invention constructs a composite gel-like hole transport material by combining polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers. Polyacrylamide, as a flexible polymer matrix, provides a stretchable network framework and good interfacial compatibility. Lithium chloride not only effectively enhances the overall conductivity of the material as an ionic conductor, but its strong hydration further enhances the interaction between the colloidal phase and water molecules, thus significantly improving the mechanical stability of the material. The PEDOT:PSS-coated cellulose nanofibers simultaneously play a dual role in nano-reinforcement and conductive network construction: the cellulose nanofibers introduce abundant hydrogen bonding sites at the microscopic level, significantly improving the tensile strength and toughness of the material, while the PEDOT:PSS coating on their surface forms a continuous and efficient charge transport pathway in the system, synergistically improving hole mobility. In summary, the synergistic effect of these three components greatly improves the conductivity, mechanical strength, and environmental stability of the composite hole transport material.

[0049] The composite hole transport material provided by this invention, when applied to flexible perovskite solar cells, exhibits excellent mechanical flexibility and high interfacial adhesion, effectively buffering bending stress and suppressing microcrack formation and interfacial delamination. This significantly improves the repeated bending resistance and mechanical reliability of flexible perovskite solar cells. Simultaneously, it facilitates efficient and stable hole extraction and transport, reducing interfacial recombination losses. Therefore, flexible perovskite solar cells using this composite hole transport material maintain excellent photoelectric conversion efficiency and operational stability even after multiple bending cycles, resulting in a significant improvement in overall performance.

[0050] Furthermore, based on the total mass of the composite hole transport material, the mass percentage of lithium chloride is 5%-25%, for example, it can be 5%, 10%, 15%, 20%, or 25%, etc. + and Cl - When dissolved in PEDOT:PSS / CNF aqueous dispersion, it undergoes dissociation and hydration, enhancing conductivity. At the same time, the appropriate amount of LiCl significantly increases the interaction between the colloidal phase and water molecules, improving mechanical properties.

[0051] Furthermore, based on the total mass of the composite hole transport material, the mass percentage of polyacrylamide is 15%-45%, for example, it can be 15%, 20%, 25%, 30%, 35%, 40%, or 45%. Polyacrylamide mainly serves as the core framework material for constructing the three-dimensional hydrogel network, responsible for providing excellent flexibility, stretchability, and structural stability.

[0052] Furthermore, in the composite hole transport material, the mass ratio of polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers is (0.3-0.6):(0.08-0.5):1, wherein the polyacrylamide is selected in the range of "0.3-0.6", for example, 0.3, 0.4, 0.5, or 0.6, and the lithium chloride is selected in the range of "0.08-0.5", for example, 0.08, 0.1, 0.2, 0.3, 0.4, or 0.5.

[0053] This invention employs polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers in a synergistic manner as hole transport materials. Under appropriate mass ratio control, not only can the material achieve good conductivity, but it can also provide the flexibility and stretchability required for flexible perovskite solar cells.

[0054] Furthermore, in the PEDOT:PSS-coated cellulose nanofibers, the mass ratio of PEDOT:PSS to cellulose nanofibers is 1:(1.2-1.8), for example, it can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, or 1:1.8. An appropriate mass ratio facilitates the full polymerization reaction of PEDOT:PSS and cellulose nanofibers via the free radicals of the EDOT monomer. Hydrogen bonds are formed between the carboxyl groups of the cellulose nanofibers and the sulfonyl groups of the PSS chains, thereby enhancing the tensile strength of the material.

[0055] Furthermore, in the PEDOT:PSS-coated cellulose nanofibers, the diameter of the cellulose nanofibers is 20nm-80nm, for example, 20nm, 40nm, 60nm, or 80nm, and the length is 500nm-1500nm, for example, 500nm, 800nm, 1000nm, 1200nm, or 1500nm. Cellulose nanofibers with specific parameters are beneficial for enhancing the mechanical and tensile properties of materials.

[0056] In another specific embodiment, the present invention provides a method for preparing the composite hole transport material for flexible perovskite solar cells as described above, the method comprising the following steps: Prepare a PEDOT:PSS-coated cellulose nanofiber suspension.

[0057] The cellulose nanofiber suspension coated with PEDOT:PSS, acrylamide monomer, and lithium chloride were mixed to obtain a dispersion.

[0058] The dispersion, crosslinking agent, initiator and catalyst are mixed and polymerized to obtain the composite hole transport material.

[0059] Furthermore, the preparation steps of the PEDOT:PSS-coated cellulose nanofiber suspension include: (a) Cellulose nanofibers, 3,4-ethylenedioxythiophene, sodium polystyrene sulfonate and an oxidant are mixed and oxidized to obtain an intermediate solution.

[0060] (b) The intermediate solution, oxidant and initiator are mixed and reacted to obtain a cellulose nanofiber suspension coated with PEDOT:PSS.

[0061] In this invention, the purpose of the oxidation treatment in step (a) is to oxidize the carboxyl groups of cellulose nanofibers to form hydrogen bonds with the sulfonyl groups of sodium polystyrene sulfonate, thereby enhancing the tensile strength of the material.

[0062] Furthermore, the concentration of the PEDOT:PSS-coated cellulose nanofiber suspension is 0.4wt%-0.6wt%, for example, it can be 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, or 0.6wt%.

[0063] Furthermore, the volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:(2-4) g:(0.5-3) g, wherein the acrylamide monomer is selected from the range of "(2-4) g", for example, 2 g, 3 g, or 4 g, and the lithium chloride is selected from the range of "(0.5-3) g", for example, 0.5 g, 1 g, 1.5 g, 2 g, 2.5 g, or 3 g.

[0064] Furthermore, the polymerization reaction temperature is room temperature. For example, room temperature can be 25±5℃, such as 20℃, 25℃, or 30℃.

[0065] Furthermore, the polymerization reaction time is 20 min to 40 min, for example, it can be 20 min, 30 min or 40 min.

[0066] Furthermore, the preparation method includes the following steps: (1) Preparation of PEDOT:PSS-coated cellulose nanofiber suspension, the preparation steps include: (a) 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate are added to cellulose nanofibers to obtain a mixture; the mixture is oxidized under stirring conditions with an oxidant to obtain an intermediate solution; wherein the oxidant includes tetramethylpiperidine oxide.

[0067] (b) An oxidant and an initiator are added to the intermediate solution and stirred and mixed. The mixture is then reacted at room temperature (e.g., 15-25°C, such as 15°C, 20°C, or 25°C) for 16-20 hours (e.g., 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours). After the reaction is completed, the mixture is washed and sonicated to obtain a PEDOT:PSS-coated cellulose nanofiber suspension. The oxidant includes ferric chloride, the initiator includes ammonium persulfate, and the concentration of the PEDOT:PSS-coated cellulose nanofiber suspension is 0.4 wt%-0.6 wt%.

[0068] (2) Acrylamide was added to the cellulose nanofiber suspension coated with PEDOT:PSS, and then lithium chloride was added and stirred to obtain a dispersion.

[0069] The volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:(2-4) g:(0.5-3) g.

[0070] (3) Under stirring conditions, a crosslinking agent, an initiator and a catalyst are added to the dispersion and mixed. Then, a polymerization reaction is carried out at room temperature for 20 min-40 min to obtain a composite hole transport material.

[0071] The crosslinking agent includes methylenebisacrylamide, the initiator includes ammonium persulfate, and the catalyst includes tetramethylethylenediamine.

[0072] In another specific embodiment, the present invention provides a flexible perovskite solar cell, the flexible perovskite solar cell comprising a flexible conductive substrate, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer and electrodes stacked together.

[0073] The hole transport layer is made of the composite hole transport material for flexible perovskite solar cells as described above.

[0074] The composite hole transport material provided by this invention, when applied to flexible perovskite solar cells, exhibits excellent mechanical flexibility and high interfacial adhesion, effectively buffering bending stress and suppressing microcrack formation and interfacial delamination. This significantly improves the repeated bending resistance and mechanical reliability of flexible perovskite solar cells. Simultaneously, it facilitates efficient and stable hole extraction and transport, reducing interfacial recombination losses. Therefore, flexible perovskite solar cells using this composite hole transport material maintain excellent photoelectric conversion efficiency and operational stability even after multiple bending cycles, resulting in a significant improvement in overall performance.

[0075] Furthermore, the material of the flexible conductive substrate includes any one of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or colorless polyimide (CPI).

[0076] Furthermore, the thickness of the hole transport layer is 30nm-50nm, for example, it can be 30nm, 40nm or 50nm.

[0077] Furthermore, the chemical formula of the perovskite light-absorbing layer is ABX3, wherein A includes any one or a combination of at least two of formamidinium ions, methylamine ions, cesium ions, or rubidium ions; B includes any one or a combination of at least two of lead ions, tin ions, or germanium ions; and X includes any one or a combination of at least two of chloride ions, bromide ions, or iodide ions.

[0078] Furthermore, the thickness of the perovskite light-absorbing layer is 400nm-700nm, for example, it can be 400nm, 500nm, 600nm or 700nm.

[0079] Furthermore, the electron transport layer is made of an n-type semiconductor material, which includes Cn... 60 Any one of PCBM, TiO2, SnO2, ZnO, or ZnO-ZnS.

[0080] Furthermore, the thickness of the electron transport layer is 10nm-20nm, for example, it can be 10nm, 15nm or 20nm.

[0081] Furthermore, a hole-blocking layer is provided between the electron transport layer and the electrode.

[0082] Furthermore, the hole blocking layer includes a BCP layer.

[0083] Furthermore, the electrode includes any one of an Al electrode, an Au electrode, an Ag electrode, or a carbon electrode.

[0084] Furthermore, the thickness of the electrode is 80nm-100nm, for example, it can be 80nm, 90nm or 100nm.

[0085] In another specific embodiment, the present invention provides a method for fabricating a flexible perovskite solar cell as described above, the method comprising the following steps: (i) Provide a flexible conductive substrate.

[0086] (ii) The composite hole transport material is added to deionized water to prepare a hole transport layer solution with a concentration of 60-70 mg / mL.

[0087] The hole transport layer solution is spin-coated onto the flexible conductive substrate and then annealed to obtain the hole transport layer.

[0088] (iii) A perovskite light-absorbing layer, an electron transport layer, a hole-blocking layer, and an electrode are sequentially fabricated on the hole transport layer.

[0089] Furthermore, the spin coating rate is 4000rpm-6000rpm, for example, it can be 4000rpm, 5000rpm or 6000rpm, and the spin coating time is 40s-60s, for example, it can be 40s, 50s or 60s.

[0090] Furthermore, the annealing temperature is 140℃-160℃, for example, it can be 140℃, 150℃ or 160℃, etc., and the annealing time is 10min-20min, for example, it can be 10min, 15min or 20min, etc.

[0091] It should be noted that the room temperature below refers to 25℃.

[0092] Example 1 This embodiment provides a composite hole transport material for flexible perovskite solar cells, the composite hole transport material comprising polyacrylamide, lithium chloride, and cellulose nanofibers coated with PEDOT:PSS.

[0093] In this process, based on the total mass of the composite hole transport material, the mass percentage of lithium chloride is 10%, and the mass percentage of polyacrylamide is 30%; the mass ratio of polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers is 0.5:0.16:1; the mass ratio of PEDOT:PSS to cellulose nanofibers in the PEDOT:PSS-coated cellulose nanofibers is 1:1.5; and the diameter of the cellulose nanofibers in the PEDOT:PSS-coated cellulose nanofibers is 20-80 nm, and the length is 500-1500 nm.

[0094] This embodiment also provides a method for preparing the composite hole transport material for flexible perovskite solar cells as described above, the preparation method comprising the following steps: (1) Preparation of PEDOT:PSS-coated cellulose nanofiber suspension, the preparation steps include: (a) Add 0.2 mL of 3,4-ethylenedioxythiophene and 0.21 mL of sodium polystyrene sulfonate to 0.3 g of cellulose nanofibers to obtain a mixture; add 0.2 g of tetramethylpiperidine oxide to the mixture under stirring for 15 min to obtain an intermediate solution.

[0095] (b) 1.36 mg of ferric chloride and 5.484 g of ammonium persulfate were added to the intermediate solution and stirred at 500 rpm for 30 min. The mixture was then reacted at 20 °C for 18 h. After the reaction was completed, the mixture was washed twice by centrifugation with a methanol / water mixture (mass ratio of 1:1), followed by three washes with deionized water. Finally, the mixture was sonicated for 10 min to obtain a PEDOT:PSS-coated cellulose nanofiber suspension with a concentration of 0.5 wt%.

[0096] (2) Add 3g of acrylamide to 6mL of the PEDOT:PSS-coated cellulose nanofiber suspension, and then add 1g of lithium chloride and stir for 30min to obtain a dispersion.

[0097] The volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:3 g:1 g.

[0098] (3) Under the stirring conditions of an ice-water bath, 100 μL of methylenebisacrylamide, 140 μL of ammonium persulfate and 30 μL of tetramethylethylenediamine were added to the dispersion and mixed for 3 min. Then, a polymerization reaction was carried out at room temperature for 30 min to obtain the composite hole transport material.

[0099] This embodiment also provides a flexible perovskite solar cell, which includes a flexible conductive substrate, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer, a hole blocking layer, and electrodes stacked together.

[0100] The hole transport layer is made of the composite hole transport material for flexible perovskite solar cells as described above; the thickness of the hole transport layer is 40 nm; the flexible conductive substrate is PEN; and the chemical formula of the perovskite light-absorbing layer is Cs. 0.05 MA 0.1 FA 0.85 PbI3, with a thickness of 500 nm; the electron transport layer is C. 60 The layer has a thickness of 12nm; the hole blocking layer is a BCP layer with a thickness of 8nm; the electrode is an Ag electrode with a thickness of 90nm.

[0101] This embodiment also provides a method for fabricating the above-mentioned flexible perovskite solar cell, including the following steps: (i) Provide a PEN film attached to an ITO substrate as a flexible conductive substrate.

[0102] The flexible conductive substrate is cleaned by ultrasonic cleaning with detergent, deionized water, acetone and anhydrous ethanol respectively, and then dried with a nitrogen gun; wherein the ultrasonic cleaning power is 100 Hz and the ultrasonic cleaning time is 15 min.

[0103] (ii) The composite hole transport material provided above is added to deionized water to prepare a hole transport layer solution with a concentration of 65 mg / mL.

[0104] The hole transport layer solution was dropped onto the flexible conductive substrate and spin-coated at 5000 rpm for 50 seconds, followed by annealing at 150°C for 15 minutes to obtain the hole transport layer.

[0105] (iii) Preparation of a perovskite light-absorbing layer, the steps of which include: 108.33 mg CsI, 1218.34 mg FAI, 132.50 mg MAI, 4033.76 mg PbI2, and 83.27 mg MACl were added to a mixed solvent consisting of 4200 μL DMF (N,N-dimethylformamide) and 840 μL DMSO (dimethyl sulfoxide), and stirred for 12 h to obtain CsI with a concentration of 1.67 mol / L. 0.05 MA 0.1 FA 0.85 PbI3 precursor solution.

[0106] A perovskite precursor solution was dropwise added to the hole transport layer, and spin-coated at 5000 rpm for 50 s with an acceleration of 1000 rpm / s. At the 35th s mark, 200 μL of chlorobenzene was added as an antisolvent. After spin-coating, the mixture was annealed at 120 °C for 15 min to obtain the chemical formula Cs. 0.05 MA 0.1 FA 0.85 PbI3 perovskite light-absorbing layer.

[0107] (iv) C is deposited on the perovskite light-absorbing layer by vacuum evaporation. 60 Layer; wherein, the parameters of the vacuum evaporation method include: an ambient vacuum degree of 5 × 10⁻⁶. -4 Pa, with an evaporation rate of 0.15 Å / s and a thickness of 12 nm.

[0108] (v) By means of a thermal evaporation process, in the C 60 An Ag electrode is deposited on the layer; wherein the parameters of the thermal evaporation process include: an ambient vacuum of 5 × 10⁻⁶. -4 Pa, with an evaporation rate of 2 Å / s and a thickness of 90 nm.

[0109] Example 2 The difference between this embodiment and embodiment 1 is that the amount of lithium chloride added in step (2) is 0.5g, so that the mass ratio of lithium chloride in the composite hole transport material is 5%.

[0110] The remaining preparation methods and parameters are consistent with those in Example 1.

[0111] Example 3 The difference between this embodiment and embodiment 1 is that the amount of lithium chloride added in step (2) is 3g, so that the mass ratio of lithium chloride in the composite hole transport material is 25%.

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 4 The difference between this embodiment and embodiment 1 is that the amount of lithium chloride added in step (2) is 0.1g, so that the mass ratio of lithium chloride in the composite hole transport material is 1%.

[0114] The remaining preparation methods and parameters are consistent with those in Example 1.

[0115] Example 5 The difference between this embodiment and embodiment 1 is that the amount of lithium chloride added in step (2) is 4g, so that the mass ratio of lithium chloride in the composite hole transport material is 30%.

[0116] The remaining preparation methods and parameters are consistent with those in Example 1.

[0117] Example 6 The difference between this embodiment and embodiment 1 is that the amount of acrylamide added in step (2) is adjusted so that the mass ratio of polyacrylamide in the composite hole transport material is 5%.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Example 7 The difference between this embodiment and embodiment 1 is that the amount of acrylamide added in step (2) is adjusted so that the mass ratio of polyacrylamide in the composite hole transport material is 55%.

[0120] The remaining preparation methods and parameters are consistent with those in Example 1.

[0121] Example 8 The difference between this embodiment and Embodiment 1 is that the mass ratio of PEDOT:PSS to cellulose nanofibers in the PEDOT:PSS-coated cellulose nanofibers is 1:1.

[0122] The remaining preparation methods and parameters are consistent with those in Example 1.

[0123] Example 9 The difference between this embodiment and Embodiment 1 is that the mass ratio of PEDOT:PSS to cellulose nanofibers in the PEDOT:PSS-coated cellulose nanofibers is 1:2.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Example 10 The difference between this embodiment and Embodiment 1 is that the thickness of the hole transport layer is 20 nm.

[0126] The remaining preparation methods and parameters are consistent with those in Example 1.

[0127] Example 11 The difference between this embodiment and Embodiment 1 is that the thickness of the hole transport layer is 100 nm.

[0128] The remaining preparation methods and parameters are consistent with those in Example 1.

[0129] Comparative Example 1 The difference between this comparative example and Example 1 is that the composite hole transport material is replaced with pure PEDOT:PSS material, that is, the hole transport layer in the flexible perovskite solar cell is a PEDOT:PSS layer, and the preparation steps of the PEDOT:PSS layer include: A 65 mg / mL PEDOT:PSS solution was dropped onto the flexible conductive substrate and spin-coated at 5000 rpm for 50 s, followed by annealing at 150 °C for 15 min to obtain a hole transport layer.

[0130] The remaining preparation methods and parameters are consistent with those in Example 1.

[0131] Figure 1 The comparison UV spectra of the perovskite light-absorbing layers prepared in Example 1 and Comparative Example 1 are shown. As can be seen from the figure, the UV absorption peak of the perovskite light-absorbing layer formed on the basis of the hole transport layer prepared by the composite hole transport layer material is slightly red-shifted. This is because the passivation groups (hydroxyl groups, ketone groups, etc.) contained in the modified hole transport layer can reduce defects and promote the crystallization of the perovskite film, so that the size of the final perovskite is larger.

[0132] Figure 2The comparative fluorescence spectra of the perovskite absorber layers prepared in Example 1 and Comparative Example 1 are shown. As can be seen from the figure, the perovskite absorber layer formed on the basis of the hole transport layer prepared by conventional PEDOT:PSS material exhibits a very high PL intensity. However, the PL quenching of the perovskite absorber layer formed on the basis of the hole transport layer prepared by the composite hole transport layer material is significantly enhanced. Quenching is considered to be the hole charge transfer from the perovskite absorber layer to the hole transport layer, thereby reducing the radiative relaxation from the excited state to the ground state. This indicates that the composite hole transport layer material provided by the present invention effectively promotes hole separation at the hole transport layer / perovskite interface.

[0133] Comparative Example 2 The difference between this comparative example and Example 1 is that the composite hole transport material does not contain lithium chloride.

[0134] The remaining preparation methods and parameters are consistent with those in Example 1.

[0135] Comparative Example 3 The difference between this comparative example and Example 1 is that the composite hole transport material does not contain polyacrylamide.

[0136] The remaining preparation methods and parameters are consistent with those in Example 1.

[0137] Comparative Example 4 The difference between this comparative example and Example 1 is that the cellulose nanofibers coated with PEDOT:PSS in the composite hole transport material are replaced with PEDOT:PSS, that is, no cellulose nanofibers are introduced.

[0138] The remaining preparation methods and parameters are consistent with those in Example 1.

[0139] Performance testing The photoelectric performance and bending resistance of the flexible titanium dioxide solar cells provided in the above embodiments and comparative examples were tested.

[0140] The test conditions for photoelectric performance testing are: AM1.5, 1000W / m 2 , 25±2℃.

[0141] The method for testing bending resistance is as follows: at room temperature of 25℃, the sample to be tested is repeatedly bent with a bending radius of 5mm using a PR-BDM-100 bending tester (PURE Materials). After a total of 3000 bends, its photoelectric conversion efficiency is measured and the retention rate relative to the initial value is calculated.

[0142] The test results are shown in Table 1.

[0143] Table 1 analyze: As shown in Table 1, this invention constructs a composite gel-like hole transport material by combining polyacrylamide, lithium chloride, and PEDOT:PSS-coated cellulose nanofibers. Polyacrylamide, as a flexible polymer matrix, provides a stretchable network framework and good interfacial compatibility. Lithium chloride not only effectively enhances the overall conductivity of the material as an ionic conductor, but its strong hydration further enhances the interaction between the colloidal phase and water molecules, thus significantly improving the mechanical stability of the material. The PEDOT:PSS-coated cellulose nanofibers simultaneously play a dual role in nano-reinforcement and conductive network construction: the cellulose nanofibers introduce abundant hydrogen bonding sites at the microscopic level, significantly improving the tensile strength and toughness of the material, while the PEDOT:PSS coating on their surface forms a continuous and efficient charge transport pathway in the system, synergistically improving hole mobility. In summary, the synergistic effect of these three components greatly improves the conductivity, mechanical strength, and environmental stability of the composite hole transport material.

[0144] The composite hole transport material provided by this invention, when applied to flexible perovskite solar cells, exhibits excellent mechanical flexibility and high interfacial adhesion, effectively buffering bending stress and suppressing microcrack formation and interfacial delamination. This significantly improves the repeated bending resistance and mechanical reliability of flexible perovskite solar cells. Simultaneously, it facilitates efficient and stable hole extraction and transport, reducing interfacial recombination losses. Therefore, the photoelectric conversion efficiency of flexible perovskite solar cells using this composite hole transport material can reach 23.7%. Even after multiple bending cycles, it maintains excellent photoelectric conversion efficiency, decreasing by only 8.8% compared to the initial efficiency.

[0145] As can be seen from the comparison between Example 1 and Examples 4-5, if the mass proportion of lithium chloride in the composite hole transport material is too small, the conductivity of the material will be weakened, thereby affecting the current of the battery; if the mass proportion of lithium chloride in the composite hole transport material is too large, it will lead to uneven cross-linking of polymer chains, loose and fragile network, and decreased mechanical properties, indirectly affecting battery efficiency.

[0146] As can be seen from the comparison between Example 1 and Examples 6-7, if the mass proportion of polyacrylamide in the composite hole transport material is too small, it is insufficient to construct a continuous and stable network structure, resulting in poor gel mechanical properties; if the mass proportion of polyacrylamide in the composite hole transport material is too large, it will lead to excessive cross-linking of polymer chains, loss of the material's inherent flexibility and tensile strength, and also easily lead to a decrease in conductivity.

[0147] A comparison of Examples 1 and 8-9 shows that if the mass ratio of PEDOT:PSS to cellulose nanofibers in the PEDOT:PSS-coated cellulose nanofibers is too large, a small amount of cellulose nanofibers will not be enough to increase the number of hydrogen bond sites on the molecular chain at the microscopic level, resulting in a decrease in the mechanical properties of the material. If the mass ratio of PEDOT:PSS to cellulose nanofibers in the PEDOT:PSS-coated cellulose nanofibers is too small, a large amount of cellulose nanofibers will seriously affect the transport of charge carriers, thereby affecting the battery efficiency.

[0148] As can be seen from the comparison between Example 1 and Examples 10-11, if the thickness of the hole transport layer is too small, the coverage will be insufficient, pinholes will be easily generated, and the perovskite layer and the electrode will be in direct contact, causing serious interfacial charge recombination and a decrease in efficiency. If the thickness of the hole transport layer is too large, the charge extraction path will be longer, which will lead to a decrease in charge extraction efficiency and affect the current and efficiency.

[0149] As can be seen from the comparison between Example 1 and Comparative Example 1, if the hole transport layer is a PEDOT:PSS layer, the switching voltage, current, FF, efficiency, and bending performance all deteriorate.

[0150] As can be seen from the comparison between Example 1 and Comparative Example 2, if the composite hole transport material does not contain lithium chloride, the conductivity of the gel material will be severely reduced, thereby affecting the battery efficiency.

[0151] As can be seen from the comparison between Example 1 and Comparative Example 3, if the composite hole transport material does not contain polyacrylamide, it cannot form a complete gel material, which is insufficient to construct a continuous and stable network structure, resulting in poor gel mechanical properties.

[0152] As can be seen from the comparison between Example 1 and Comparative Example 4, if the composite hole transport material does not introduce cellulose nanofibers, it is insufficient to increase the number of hydrogen bond positions of the molecular chain at the microscopic level, resulting in a decrease in the mechanical properties of the material.

[0153] It should be noted that the technical solution of the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite hole transport material for flexible perovskite solar cells, characterized in that, The composite hole transport material comprises polyacrylamide, lithium chloride, and cellulose nanofibers coated with PEDOT:PSS.

2. The composite hole transport material according to claim 1, characterized in that, Based on the total mass of the composite hole transport material, the mass percentage of lithium chloride is 5%-25%.

3. The composite hole transport material according to claim 1 or 2, characterized in that, Based on the total mass of the composite hole transport material, the mass percentage of the polyacrylamide is 15%-45%. And / or, in the composite hole transport material, the mass ratio of polyacrylamide, lithium chloride and PEDOT:PSS-coated cellulose nanofibers is (0.3-0.6):(0.08-0.5):1; And / or, in the PEDOT:PSS-coated cellulose nanofibers, the mass ratio of PEDOT:PSS to cellulose nanofibers is 1:(1.2-1.8); And / or, in the PEDOT:PSS-coated cellulose nanofibers, the diameter of the cellulose nanofibers is 20nm-80nm and the length is 500nm-1500nm.

4. A method for preparing a composite hole transport material for flexible perovskite solar cells as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: Preparation of PEDOT:PSS-coated cellulose nanofiber suspension; The PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride were mixed to obtain a dispersion. The dispersion, crosslinking agent, initiator and catalyst are mixed and polymerized to obtain the composite hole transport material.

5. The preparation method according to claim 4, characterized in that, The preparation steps of the PEDOT:PSS-coated cellulose nanofiber suspension include: (a) Cellulose nanofibers, 3,4-ethylenedioxythiophene, sodium polystyrene sulfonate and an oxidant were mixed and oxidized to obtain an intermediate solution; (b) The intermediate solution, oxidant and initiator are mixed and reacted to obtain a cellulose nanofiber suspension coated with PEDOT:PSS.

6. The preparation method according to claim 4 or 5, characterized in that, The concentration of the PEDOT:PSS-coated cellulose nanofiber suspension is 0.4wt%-0.6wt%. And / or, the volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:(2-4) g:(0.5-3) g.

7. The preparation method according to any one of claims 4-6, characterized in that, The polymerization reaction temperature is room temperature; And / or, the polymerization reaction takes 20 min to 40 min.

8. The preparation method according to any one of claims 4-7, characterized in that, The preparation method includes the following steps: (1) Preparation of PEDOT:PSS-coated cellulose nanofiber suspension, the preparation steps include: (a) 3,4-ethylenedioxythiophene and sodium polystyrene sulfonate are added to cellulose nanofibers to obtain a mixture; the mixture is oxidized under stirring conditions with an oxidant to obtain an intermediate solution; wherein the oxidant includes tetramethylpiperidine oxide; (b) An oxidant and an initiator are added to the intermediate solution and stirred and mixed. The mixture is then reacted at room temperature for 16-20 hours. After the reaction is completed, the mixture is washed and sonicated to obtain a PEDOT:PSS-coated cellulose nanofiber suspension. The oxidant includes ferric chloride, the initiator includes ammonium persulfate, and the concentration of the PEDOT:PSS-coated cellulose nanofiber suspension is 0.4 wt%-0.6 wt%. (2) Acrylamide was added to the cellulose nanofiber suspension coated with PEDOT:PSS, and then lithium chloride was added and stirred to obtain a dispersion. The volume-to-mass ratio of the PEDOT:PSS-coated cellulose nanofiber suspension, acrylamide monomer, and lithium chloride is 6 mL:(2-4) g:(0.5-3) g. (3) Under stirring conditions, a crosslinking agent, an initiator and a catalyst are added to the dispersion and mixed. Then, a polymerization reaction is carried out at room temperature for 20 min-40 min to obtain a composite hole transport material. The crosslinking agent includes methylenebisacrylamide, the initiator includes ammonium persulfate, and the catalyst includes tetramethylethylenediamine.

9. A flexible perovskite solar cell, characterized in that, The flexible perovskite solar cell includes a flexible conductive substrate, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer, and electrodes stacked together. The material of the hole transport layer is the composite hole transport material for flexible perovskite solar cells as described in any one of claims 1-3.

10. The flexible perovskite solar cell according to claim 9, characterized in that, The flexible conductive substrate is made of any one of polyethylene terephthalate, polyethylene naphthalate, or colorless polyimide. And / or, the thickness of the hole transport layer is 30nm-50nm; And / or, the chemical formula of the perovskite light-absorbing layer is ABX3, wherein A includes any one or a combination of at least two of formamidinium ions, methylamine ions, cesium ions or rubidium ions, B includes any one or a combination of at least two of lead ions, tin ions or germanium ions, and X includes any one or a combination of at least two of chloride ions, bromide ions or iodide ions. And / or, the thickness of the perovskite light-absorbing layer is 400nm-700nm; And / or, the material of the electron transport layer is an n-type semiconductor material, the n-type semiconductor material including C 60 Any one of PCBM, TiO2, SnO2, ZnO, or ZnO-ZnS; And / or, the electrode includes any one of an Al electrode, an Au electrode, an Ag electrode, or a carbon electrode.

Images